The hydrogenated product of aromatic polycarboxylic acid has been widely used as the raw material for functional polyimide and functional epoxy resin. With recent demand for more valuable functional resin, a hydrogenated product of aromatic polycarboxylic acid with high purity comes to be required. In particular, in an application field requiring high transparency, a hydrogenated product of aromatic polycarboxylic acid having the remaining amount of aromatic ring reduced as low as possible comes to be keenly demanded.
As the production method of a high-purity hydrogenated product of aromatic polycarboxylic acid, (i) a method of directly nuclear-hydrogenating an aromatic polycarboxylic acid (for example, Non-Patent Document 1 and Patent Documents 1 to 4) and (ii) a method in which an aromatic polycarboxylic acid is converted to its ester and then the ester is nuclear-hydrogenated (for example, Patent Documents 5 and 6) have been proposed.
Non-Patent Document 1 discloses (i) a method of nuclear-hydrogenating pyromellitic acid under a hydrogen pressure of 2.7 atm at 60° C. in the presence of a catalyst comprising 5% of rhodium metal supported on a carbon support (amount of rhodium metal used: 2% by weight of the starting compound) and (ii) a method of nuclear-hydrogenating phthalic acid, isophthalic acid, and terephthalic acid at 60 to 70° C. in the presence of a catalyst comprising 5% of rhodium metal supported on an alumina support (amount of rhodium metal used: 2.4% or 0.6% by weight of the starting compound).
Since a large amount of catalyst is used in both the methods mentioned above, the conversion and selectivity of the aromatic polycarboxylic acid are not necessarily sufficient and the starting aromatic polycarboxylic acid is likely to remain not hydrogenated.
Patent Document 1 proposes a method of nuclear-hydrogenating an aromatic polycarboxylic acid in the presence of a catalyst comprising rhodium metal and/or palladium metal in batchwise manner (amount of noble metal used: 0.5 to 10 parts by weight per 100 parts by weight of the aromatic polycarboxylic acid).
In the examples thereof, however, only the catalyst comprising 0.5% by weight, 2% by weight, or 5% by weight of rhodium supported on carbon and the catalyst comprising 5% by weight of palladium supported on carbon are used, and the nuclear hydrogenation in the presence of a catalyst comprising both rhodium and palladium is not described. The ability of reusing catalyst, which is important for industrial economy, is evaluated only by the reaction up to 9 times recycles.
Patent Document 2 proposes a method of nuclear-hydrogenating an aromatic polycarboxylic acid in the presence of a catalyst comprising 5% of rhodium metal supported on γ-alumina support having a specific surface area of 50 to 450 m2/g (amount of rhodium metal used: 0.25 part by weight or more and less than 0.5 part by weight per 100 parts by weight of the aromatic polycarboxylic acid).
Patent Document 2 describes that the reduction of catalyst activity is very small or hardly found even when the catalyst is continuously used in the nuclear hydrogenation without the activation treatment after every run of reaction (paragraph 0036). However, Patent Document 4 describes in comparative example 3 that when the nuclear hydrogenation is repeated using a catalyst comprising rhodium metal supported on γ-alumina support having a specific surface area of 150 m2/g without the activation treatment, the catalyst activity reduces and the conversion is extremely reduced in fourth run of the batchwise nuclear hydrogenation, thereby allowing a large amount of aromatic polycarboxylic acid to remain not hydrogenated. Therefore, the catalyst taught by Patent Document 2 does not endure the repeated use in a long period of time. In addition, it is economically very disadvantageous to change the highly expensive rhodium metal catalyst frequently for repeating the reaction.
Patent Document 3 proposes a method of nuclear-hydrogenating an aromatic polycarboxylic acid in the presence of a catalyst comprising one or more noble metals selected from ruthenium, rhodium, palladium, and platinum supported on an alumina, silica, or silica alumina support (amount of noble metal used: 0.05 to 0.45% by weight of the aromatic polycarboxylic acid).
However, only a rhodium alumina catalyst is used in the examples of Patent Document 3. The rhodium alumina catalyst is similar to the catalyst proposed by Patent Document 2. Like the catalyst of Patent Document 2, therefore, the rhodium alumina catalyst of Patent Document 3 is difficult to repeatedly use for a long period of time and economically disadvantageous.
Patent Document 4 describes that the decrease in the conversion and the degradation of catalyst can be prevented by conducting the nuclear hydrogenation at a limited range of temperature and further describes that the number of repeated use can be increased by an effective activation treatment.
In the examples of Patent Document 4, the rhodium catalyst is repeatedly used in the reaction. However, the number of repeated use is limited to about 10 times, and therefore, the catalyst is still economically disadvantageous.
Patent Documents 5 and 6 describe the method of converting an aromatic polycarboxylic acid to its ester and then nuclear-hydrogenating the ester.
However, the proposed method requires an additional step of converting the aromatic carboxylic acid to the ester, to elongate the overall production process and require a complicated reaction apparatus, thereby increasing production costs.    Patent Document 1: JP 2003-286222A    Patent Document 2: JP2006-83080A    Patent Document 3: JP2006-124313A    Patent Document 4: JP2008-63263A    Patent Document 5: JP8-325196A    Patent Document 6: JP8-325201A    Non-Patent Document 1: J. Org. Chem., 31, 3433 (1966)